As one of copyright protecting techniques in a DVD (Digital Versatile Disc)-ROM (Read Only Memory), a recording type DVD, and the like, in a state of a non-recorded disc, binary information which is peculiar to a medium and is called a media ID is preliminarily recorded in an innermost rim side area (called BCA (Burst Cutting Area)) and content data which is recorded is encrypted by using the media ID.
Also in a high density optical disc such as a Blu-ray disc (registered trademark; hereinbelow, referred to as BD) or the like, as disclosed in JP-A-2005-518055, such a technique that a bar-code-like mark (hereinbelow, referred to as a BCA mark) as binary information is recorded into the innermost rim side area (hereinbelow, referred to as BCA) has been proposed.
In JP-A-2005-518055, the following techniques have been disclosed: the BCA mark is recorded by using a crystalline state and an amorphous state of a phase change recording film; grooves or pits are formed in the BCA at a track pitch which is five or more times as larger as that of the adjacent area; the BCA mark is formed in the radial direction so as to traverse a plurality of tracks; and the like. Further, in JP-A-2005-518055, the following technique has been disclosed: in the case of reproducing the BCA mark, an alteration of the BCA mark is detected by comparing a reproduction waveform which is obtained when the BCA mark is reproduced by using the grooves by tracking servo control with a reproduction waveform which is obtained when the BCA mark is reproduced without making the tracking servo control.
In a recording area where a signal is recorded to a normal track, the signal is recorded or reproduced in the state where a spot of a laser beam has been in-focused to a signal surface by focusing servo control and the track is accurately traced by the tracking servo control. On the other hand, the BCA is an area which is formed in consideration of a purpose of enabling the information to be more easily read out in the state where the in-focus state according to the focusing servo control has merely been obtained without making the tracking servo control.
Also with respect to the BCA, it is assumed that grooves (that is, tracks) have been formed and a signal recording layer corresponding to the phase change system has continuously been formed from, for example, a lead-in area. In the BCA which is formed so as to have the signal recording layer corresponding to the phase change system as mentioned above, the BCA mark can be formed as follows.
For example, at the manufacturing stage, in the state before initialization, the signal recording layer is in the amorphous state. For example, with respect to a data area, by executing the initialization by irradiating a laser beam by, for instance, a red high-power laser to the whole area, the layer is changed from the amorphous state to the crystalline state. The signal recording layer of the BCA is also in the amorphous state before the initialization. In association with the initialization, the signal recording layer is not set into the crystalline state by initializing the whole BCA but is set into the crystalline state by irradiating the laser beam only to a desired portion in the circumferential direction in correspondence to the BCA mark, for example, a pattern of a bar code corresponding to the contents of a disc ID. As a result of such a step, in the BCA, the information recording in a bar code form by a pattern based on a bar portion in the amorphous state of a predetermined width along the circumferential direction and a bar portion in the crystalline state is executed.
In recent years, to increase a memory capacity in a recordable DVD or a high-density optical disc, a recording and reproducing format of a multi-layer disc has been proposed. In a high-density optical disc of two layers, for example, a BD of two layers, the BCA mark is recorded into an information layer locating on the rear side of the information reading side (referred to as an L0 layer; an information layer locating on this side is referred to as an L1 layer).
FIG. 14 shows an example of a waveform of a reproduction signal of the BCA mark of such a double-layer BD (in the case where the tracking servo control is not made). In the crystalline state, since a reflectance is high, the reproduction signal of a high level IH is obtained. In the amorphous state, since a reflectance is low, the reproduction signal of a low level IL is obtained.
However, in the high-density optical disc in the related art, for example, in the BD, when the tracking servo control is not made, a reproducing laser beam reads the BCA marks from a plurality of grooves. The signal is modulated by a diffraction which is caused by the grooves. Thus, there is such a drawback that, as shown in FIG. 14, a level fluctuation occurs in the reproduction signal of the BCA marks due to a crosstalk of a groove signal, and the signal reproduction of the BCA marks becomes unstable.
According to the standard of the BD, as a reference adapted to stably reproduce the BCA marks, it is specified that a ratio IH/IL (also, referred to as a contrast) between the high level IH and the low level IL of the reproduction signal of the BCA marks is equal to or larger than 4 times. As shown in FIG. 14, when the level fluctuation is large, it is difficult that a ratio between a minimum value IHmin of the high level and a maximum value IHmax the low level satisfies the foregoing standard value.
It is, therefore, an object of the invention to provide a record medium, its manufacturing method, a mother disc for the record medium, and its manufacturing method, in which binary information which has previously been recorded in an innermost rim side area can be stably reproduced.